1. Field of the Invention
The present invention relates generally to plasma generation and more specifically to plasma abatement methods and systems for treatment of waste emissions from a semiconductor processing chamber.
2. Description of the Related Art
Release of gases that are toxic to humans or generally harmful to the global environment, is of growing concern to industrial producers of such emissions. The semiconductor industry is one of the many industries particularly affected because the fabrication of computer chips involves toxic chemicals, e.g., arsine, phosphine, and chlorine. Other very stable compounds are also generated in semiconductor manufacturing processes that are capable of reaching the upper atmosphere and inflicting serious and long-term damage to the planetary climate. Consequently, governments worldwide are taking a more aggressive role in legislating and regulating the amount of air pollution generated by the semiconductor industry.
In the current state of the art, it is conventional to treat effluent gases from semiconductor processing with several different abatement methods, including thermal destruction, and wet and dry scrubbing. Many semiconductor companies presently use central burn tubes and scrubbers to treat the gases before they are vented to the atmosphere. However, the efficiency of thermal destruction is limited by the thermal stability of the effluent species. The high temperatures required to decompose some materials can only be achieved by using electric furnaces or reactant gases that release energy via exothermic reactions. This is especially true when abating highly stable perfluorinated compounds. Both methods use a significant amount of resources leading to high costs of ownership. Furthermore, when certain chloride compounds are exposed to high temperatures in the presence of oxygen, they can react to form extremely hazardous polychlorinated compounds. Additionally, the high temperatures reached in thermal furnaces result in a significant increase in the degradation rate of materials of construction leading to a shorter lifetime of the abatement units.
Traditional dry and wet scrubbing techniques are limited in their ability to destroy certain effluent compounds such as organic chlorides. Additionally, dry scrubbing methods use vessels containing beds of adsorbent material whose surface physically adsorbs the molecules of the effluent species being abated, but such methods produce a vessel of hazardous material for disposal. Likewise, wet scrubbing techniques produce large quantities of contaminated fluids that must be disposed as toxic waste thereby increasing the cost of the abatement system and associated semiconductor manufacturing facility.
Recently, a new generation of abatement systems have been developed using non-thermal low pressure plasma reactors. Unlike thermal systems, wherein molecular decomposition occurs via thermodynamic dissociation, non-thermal plasmas use electron-molecule collisions to dissociate molecules. Typically, these non-thermal reactors use microwave or radio frequency energy sources and must be positioned between the processing chamber and the semiconductor vacuum pump because they operate at reduced pressures. However, placement of these non-thermal plasma systems between the processing chamber and the vacuum pump, can present problems such as deposit formation, viz., the precipitation of solids in the vacuum pump, which causes clogging of the exhaust lines leaving the vacuum pump. Additionally, the positioning of the plasma abatement system near the processing chamber may adversely affect the semiconductor tool and processing.
It would, therefore, be desirable to provide an improved abatement method that does not generate highly reactive radicals, form perfluorinated greenhouse gases, precipitate blocking solids in a vacuum system and/or generate voluminous quantities of hazardous material that increase production costs, disposal costs, and exposure risks to personnel.
The present invention generally relates to plasma abatement systems and methods, and more specifically to use of low-temperature plasma to abate semiconductor process effluents.
The invention in various embodiments described hereinafter in greater detail, contemplates:
an abatement device that may be coupled into existing point of use abatement systems, such as wet, dry and thermal systems;
an abatement plasma system that is positioned after the semiconductor vacuum pump system thereby not affecting the semiconductor tool, process, or the operation of the pump;
an abatement plasma process that is conducted at atmospheric pressure thereby eliminating the need for placement of the abatement plasma chamber before a vacuum pump in the semiconductor processing system; and
an improved plasma abatement method that does not generate unnecessary amounts of a hazardous waste for disposal.
In one method aspect, the invention relates to non-thermal abatement of effluent species generated in a semiconductor processing unit, comprising the following steps:
a) introducing an effluent stream into a discharge reactor, the stream having products and unused gaseous components from a semiconductor processing chamber;
b) subjecting the effluent stream to a corona discharge in the discharge reactor; and
c) maintaining the effluent stream in the discharge reactor for a sufficient time to allow components of the effluent stream to react with energized electrons to destroy or render harmless the products and unused gaseous components. Preferably, the discharge reactor is maintained at approximately atmospheric pressure.
In another method aspect, the invention relates to the introduction of a gas mixture comprising an effluent gas stream from a semiconductor process and a reactive partner into a discharge reactor, such method comprising the steps of:
a) introducing a gas mixture into a discharge reactor, the gas mixture comprising an effluent gas stream from a semiconductor processing chamber and a reactive partner;
b) subjecting the gas mixture to a corona discharge in the discharge reactor; and
c) maintaining the gas mixture in the discharge reactor for a sufficient time to allow components of the effluent gas stream to react with energized electrons and reactive partners to destroy and/or convert the gas stream components. Preferably the reactive partners include gases that are easy sources of electrons (i.e., easily ionizable species, such as argon) and/or gases that enhance oxidative or reductive reactions of the products and unused gaseous components in the effluent stream.
A further aspect of the invention relates to a method for introducing an effluent gas stream from a semiconductor process into an abatement chamber, at approximately atmospheric pressure, wherein a corona discharge zone is created and a secondary abatement process is concurrently performed in the abatement chamber. Such abatement method comprises the steps of:
a) removing an effluent gas stream, comprising products and unused gaseous components, from a semiconductor processing chamber through a connecting vacuum system and introducing the effluent gas stream into an abatement chamber; and
b) subjecting the effluent stream to a corona discharge in the abatement chamber for a sufficient time to render harmless the components of the effluent stream while subjecting the harmless components and gas stream to a secondary abatement method for separation of gaseous and solid components.
Other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims.